Yellow spots appearing on green bean leaves can be concerning for gardeners. However, with proper identification and treatment, many common leaf spot diseases are not too serious of a threat.
This article will cover the most prevalent causes of yellow spots on green bean leaves and how to care for an affected plant.
Identifying Yellow Leaf Spot Diseases
There are a few common culprits that can cause those undesirable yellow spots on green bean leaves. Let’s take a closer look at three likely suspects:
Bean common mosaic virus
The bean common mosaic virus is one of the most prevalent viral diseases affecting green beans. It is spread primarily by certain species of aphids and seed transmission. Symptoms of this virus include mottle or mosaic leaf patterning along with yellow spots. You may also see leaf distortion.
Alternaria leaf spot
Alternaria leaf spot is a fungal disease that produces small, brown-to-black spots on the leaves, stems and pods of green beans.
These spots are smaller than those of anthracnose. They may enlarge and become circular, with tan centers and dark margins. Gray spores form in the plant spots during wet or humid weather.
Anthracnose
Anthracnose, caused by the fungus Colletotrichum lindemuthianum, is one of the most destructive leaf diseases of beans. It first appears as small, circular or irregular lesions on the leaves.
As the spots enlarge, they develop dark borders surrounded by yellow or chlorotic zones. Spores produced in beanspots can spread the disease very rapidly under favorable conditions.
Assessing the Severity of an Infestation
Once you have identified the potential culprit causing those unpleasant “yellow spots on green bean leaves”, it is important to gauge how serious the infestation may be:
Number and size of spots: the more numerous and larger the individual yellow spots, the more advanced the disease. Few isolated spots: are less worrying than widespread infection.
Overall plant health: Pay attention to symptoms on other leaves and parts of the plant. Are new spots appearing or is the plant otherwise vigorous? A significant decline likely means a more severe case.
Location on plant: Spots mainly on lower, interior leaves pose less risk than seeing them on upper and exterior foliage as well. Upper leaves are more photosynthetically active.
Progression over time: Monitor how quickly spots appear to spread. Rapidly increasing or migrating symptoms within a week most likely require treatment, versus slow, stagnant disease development.
Consider taking photos of affected leaves over 7–10 days to better track the progression of those yellow spots on green bean leaves. Faster spreading disease warrants quicker action to avoid yield or quality losses.
Treating Affected Plants
Once you have identified the causative agent and assessed the severity of those unsightly yellow spots on green bean leaves affliction, it’s time to implement a treatment regimen. Here are some effective options:
Fungicide or Antibacterial Spray
For fungal or bacterial-related spots, applying a fungicide or antibacterial spray can help stop further spread. Look for active ingredients like copper, mancozeb, and chlorothalonil. Carefully follow label instructions about rates and timing for best results.
Example products:
- Liquid Copper Fungicide Concentrate (copper octanoate)
- Ferti-lome Broad Spectrum Fungicide (mancozeb)
- Bonide Captain Jack’s Deadbug Brew (spinosad)
Improve Growing Conditions
For any disease, optimizing plant health makes treatment more effective. Ensure:
- Proper plant spacing for airflow
- Adequate but not excessive, watering
- Good drainage to avoid leaf wetness
- Maximum sunlight exposure
Remove Severely Infected Plants
As a last resort, remove and destroy any plants exhibiting very advanced yellow spots on green bean leaves that threaten surrounding foliage. If done carefully, this can prevent disease from spreading in the garden.
You might like: The Complete Guide to Green Bean Germination Time
Preventing Future “Yellow Spots on Green Bean Leaves”
Once you’ve got a handle on actively treating existing issues, the next priority is preventing recurrences of those pesky yellow spots on green bean leaves down the road. Here are some protective practices:
Crop Rotation: Moving beans (and all members of the legume family) to a new garden area every 1-2 years breaks the life cycle of soilborne pathogens.
Weed Control: Keeping the garden space neatly weeded reduces alternate hosts for diseases to overwinter or spread on.
Resistant Varieties: Choose beans labeled as resistant to common leaf spot diseases like anthracnose when available. ‘Cornell Bush Bean 49’ shows tolerance.
Proper Watering: Avoiding standing water on leaves through prudent irrigation limits conditions for fungal/bacterial growth.
Air Circulation: Allow spacing between plants and avoid overcrowding to encourage rapid drying of foliage.
Sanitation: Remove and destroy or bury deeply all severely diseased plant debris at the season’s end to eliminate inoculum sources.
Till Soil After: Till under or solarize old garden areas in autumn to expose pathogens to extremes that may kill them off before spring.
While bean leaf spots may still occur occasionally despite prevention, home gardeners can get the upper hand employing these best practices. With some diligence, you’ll be enjoying fresh, healthy harvests of green beans for many growing seasons to come!
Conclusion
As demonstrated above, those yellow spots on green bean leaves afflicting green bean plants are often caused by one of several common fungal or viral diseases.
With correct identification of the culprit, judicious assessment of severity, implementation of applicable treatments, and preventive cultural practices, gardeners can successfully manage outbreaks and keep their prized bean crops thriving.
While leaf diseases may not be fully avoidable, home growers have many tools at their disposal to tip the scales in their favor.
Whether a long-time gardener or someone new to growing beans, I hope this comprehensive guide has equipped you to better understand and deal with the yellow spots on green bean leaves dilemma.
With knowledge and proactive care, home gardens everywhere can keep enjoying pest-free picking of green beans for many seasons to come.
